782 MAMMALIA. 



circumference of the mouth. The outer row is composed of the longest 

 plates, and these are in proportion to the varying distances between the 

 two jaws, some being fourteen or fifteen feet long, and twelve or fifteen 

 inches broad; but towards the anterior and posterior part of the mouth 

 they are very short. 



(2253.) Inferiorly each plate of whalebone is terminated by a broad 

 fringe of horny fibres resembling hair ; and, seeing that in some whales 

 there are about three hundred plates composing the outer row on each 

 side of the mouth, the reader may form some idea of the extent of this 

 enormous strainer, whereby the little Clio borealis, and other small 

 Mollusca that swarm so abundantly in the Northern ocean, are caught 

 by shoals preparatory to their being swallowed. 



(2254.) For what is known concerning the growth of whalebone, we 

 are indebted to John Hunter ; and as it would be difficult to curtail 

 his clear and concise description of the process, it is here given in his 

 own words * : 



(2255.) " The formation of whalebone is extremely curious, being in 

 one respect similar to that of hair, horns, spurs, &c. ; but it has besides 

 another mode of growth and decay, equally singular. 



(2256.) " These plates form upon a thin vascular substance, not 

 immediately adhering to the jaw-bone, but having a more dense sub- 

 stance between, which is also vascular. This substance, which may be 

 called the nidus of the whalebone, sends out thin, broad processes 

 answering to each plate, on which the plate is formed, as the cock's 

 spur or the bull's horn on the bony core, or a tooth on its pulp ; so that 

 each plate is necessarily hollow at its growing end, the first part of the 

 growth taking place on the inside of this hollow. 



(2257.) " Besides this mode of growth, which is common to all such 

 substances, it receives additional layers on the outside, formed from the 

 above-mentioned vascular substance, extended along the surface of the 

 jaw. This part also forms upon it a semi-horny substance between 

 each plate, which is very white, rises with the whalebone, and becomes 

 even with the outer edge of the jaw. This intermediate substance fills 

 up the spaces between the plates as high as the jaw ; acts as abutments 

 to the whalebone ; or is similar to the alveolar processes of the teeth, 

 keeping them firm in their places. 



(2258.) "As both the whalebone and intermediate substance are 

 constantly growing, and as we must suppose a determined length neces- 

 sary, a regular mode of decay must be established, not depending 

 entirely on chance, or the use it is put to. In its growth, three parts 

 appear to be formed : one from the rising cone, which is the centre ; a 

 second on the outside ; and a third, being the intermediate substance. 

 These appear to have three stages of duration ; for that which forms on 

 the cone, I believe, makes the hair, and that on the outside makes 



* Vide supra. 



